The present invention is directed to the field of printed circuit boards. More particularly, the present invention is directed to a reusable extension mechanism and method for assembling overhanging components on a printed circuit board.
For many years, electronic systems (i.e., computers, printers, etc.) have been designed with one or more printed circuit boards (PCBs) that are electrically connected together to perform various functions. One of these printed circuit boards, which is commonly employed within computers, is referred to as a xe2x80x9cmotherboardxe2x80x9d, The motherboard typically is the main printed circuit board that provides interconnections between primary electronic components of the computer such as its processor, memory, and the like.
Businesses may follow a well-established circuit board assembly procedure in order to manufacture a fully functional circuit board. This circuit board assembly procedure may have four sequential stages of which the second, third and fourth stages are performed in an assembly line environment while the first stage is performed beforehand, normally at an off-line site, in an effort to speed up the assembly line stages. The first stage may involve programming various programmable electronic components using well-known manual or automated equipment operated by one or more persons. These programmable electronic components include, but are not limited to, read-only memory (xe2x80x9cROMxe2x80x9d), erasable programmable read-only memory (xe2x80x9cEPROMxe2x80x9d) and electrically erasable and re-programmable non-volatile memory (typically referred to as xe2x80x9cflashxe2x80x9dmemory). Afterwards, electronic components are connected to the circuit board during the second or third stages.
The second and third stages involve assembly of the circuit board by connecting surface mount technology (xe2x80x9cSMTxe2x80x9d) components followed by through hole mount technology (xe2x80x9cTHMTxe2x80x9d) components through various widely known techniques. For example, the technique for connecting SMT components to the circuit board may include the following operations: (i) solder paste application, (ii) proper placement of the SMT components, and (iii) reflow soldering to establish connections between trace lines previously routed in the circuit board and the SMT components. Likewise, the technique for connecting the THMT components may include the following operations: (i) proper placement of THMT components, and (ii) wave soldering.
The fourth stage in manufacturing circuit boards may involve testing each component (i.e., xe2x80x9cin circuitxe2x80x9d testing) as well as the entire operation of the circuit board (i.e., xe2x80x9cfunctionalxe2x80x9d testing) to determine whether the circuit board is functioning properly.
Assembly of the circuit board may involve overhanging components such as connectors, sockets, components and the like on leading or lagging edges of the PCBs. Overhanging surface mount technology (SMT) components are a challenge to assemble in the SMT board assembly process. Overhanging components may be devices that extend outward past the edge of a printed circuit assembly (PCA). Overhanging components may require a large xe2x80x9cstay outxe2x80x9d area to not interfere with SMT assembly tools such as screen print and placement machines. As such, design rules may include xe2x80x9cstay outxe2x80x9d zones that prohibit overhanging components on leading and/or lagging edges of PCAs. The leading and lagging edges are the non-conveying edges of the PCA. However, the SMT equipment xe2x80x9cstay outxe2x80x9d zone for overhanging devices may vary for different types of tools (i.e., chip shooter, component placer, screen printer) and may vary for different placement equipment vendors. The stay out zones may vary so much from different types of tools and suppliers that design rules may require that the entire leading edge of the PCA is a xe2x80x9cstay outxe2x80x9d zone for overhanging SMT components. More specifically, the board stops, tooling pins and sensors may be located in different areas on the equipment.
FIG. 1 illustrates a printed circuit assembly (PCA) having an outrigger, more specifically. FIG. 1 shows a printed circuit assembly 10 that includes an outrigger 20 affixed to the printed circuit assembly 10 by a plurality of extension bridges 25. The outrigger 20 is an extension of the printed circuit board (PCB) on leading or lagging edges that are attached by several small bridges (such as the extension bridges 25). The extension bridges 25 may be made out of the same material as the PCB and extend past the leading or lagging edge of the to-be-assembled PCB. The outrigger 20 may be made during the same manufacturing process as the printed circuit assembly 10 in one integral unit. Areas between the outrigger 20 and the printed circuit assembly 10 may be routed out to leave small connections such as the extension bridges 25. That is, routing or drilling the PCB area between the outrigger 20 and the PCA 10 creates the extension bridges 25. No routing or drilling is done where the extension bridge 25 are located. The extension bridges 25 may be drilled or routed so that the outrigger 20 can easily be separated from the PCA after SMT assembly. After assembly, the outrigger 20 may be broken off manually or cut-off by routers and discarded. FIG. 1 also shows how overhanging components 15 may hang over the outrigger 20. Outriggers may add a significant cost to the PCB. For example, each outrigger may add a total cost of between $0.20 and $3.50 to the cost of materials depending on the board size and the layer count. This makes overhanging SMT devices expensive to implement.